Acceptance testing, commissioning and routine QA of the Varian TrueBeam Richard Popple

Disclosure UAB has Varian research contracts Honorarium from Varian

Not your father s Chevy

Not your father s Chevy Linac

TrueBeam distinquishing characteristics Completely digital control system Waveguide and filter design allows 5 flattened photon energies up to 20 MV. Electron scattering foils are of a new design. Implements 6 MV and 10 MV flattening filter free (FFF) beams that provide dose rates up to 2400 monitor units per minute.

Possible Benefits of a FFF Efficiency More accurate beam modeling due to decreased head scatter Decreased leakage and dose outside field The study showed that removing the filter increased the dose rate on the central axis by a factor of 2.31 (6 MV) and 5.45 (18 MV) at a given target current. Because the flattening filter is a major source of head scatter photons, its removal from the beam line could reduce the out-of-field dose. Vassiliev ON, Titt U, Kry SF, Pönisch F, Gillin MT, Mohan R Med Physics 2006 vol. 33 (4) pp. 820-7

Unflattened Beam Has a Lower Risk of Secondary Tumors Cashmore J, Int J Radiat Oncol Biol Phys. 2011

Beam Profile Flattening Filter

Depth Dose with Flattened Beam 2004 Phys. Med. Biol. 49 1535

Calibration No difference for FFF Polarity and recombination corrections small Energy Dose rate Ppol Pion 6X 600 1.000 1.004 15X 600 1.000 1.005 6X FFF 1400 1.000 1.006 10X FFF 2400 1.000 1.013

Calibration Kry SF, Popple R, Molineu A, Followill DS. Ion recombination correction factors (P(ion)) for Varian TrueBeam high-doserate therapy beams. J Appl Clin Med Phys. 2012 Nov 8;13(6):3803. doi: 10.1120/jacmp.v13i6.3803. PubMed PMID: 23149774.

Calibration Kry SF, Popple R, Molineu A, Followill DS. Ion recombination correction factors (P(ion)) for Varian TrueBeam high-dose-rate therapy beams. J Appl Clin Med Phys. 2012 Nov 8;13(6):3803. doi: 10.1120/jacmp.v13i6.3803. PubMed PMID: 23149774.

Calibration use Pb foil for all FFF beams

Difference from 6X (%) 5 4 3 2 1 0-1 Calibration sanity check Exradin A12 EDR2 MOSFET -2 6X FFF 400 MU/min 6X FFF 1400 MU/min 6X 600 MU/min 10X FFF 400 MU/min 10X FFF 2400 MU/min 15X 600 MU/min

IROC Calibration check RPC OSLD measurement / Institution 6X FFF = 0.99 10X FFF = 0.99

Profile and depth dose correction for recombination Measured x-ray distributions of 6FFF and 15FFF beams plotted against charged collected per beam pulse. Also plotted are the results from applying corrections for the ion chamber collection efficiency. The distributions were measured at 100 cm SSD with the 0.1 cm 3 chamber at D max and biased with 300 V. S Johnsen Ion Chamber Collection Efficiency Considerations for Un-Flattened X-Ray Beams, Med. Phys. 35, 2770 (2008)

Profile and depth dose correction for recombination Measured 15 FFF x- ray depth-dose distribution and distribution resulting from corrections for ion chamber collection efficiency. Each curve is normalized to 100% at D max. Data is for a 0.1 cm 3 chamber biased to 300 V; 10x10 cm 2 field at 100 cm SSD. S Johnsen Ion Chamber Collection Efficiency Considerations for Un-Flattened X-Ray Beams, Med. Phys. 35, 2770 (2008)

FFF head scatter Cashmore Phys Med Biol 2008

FFF surface dose Vassiliev et al. Phys Med Biol 2006

Photon commissioning AAA Data requirements are the same No additional data required for FFF

10X FFF profile

IROC VMAT Spine

IROC Gated VMAT Lung

IMRT QA results 70 60 Mean=0.7% s.d.=1.1% Number of cases 50 40 30 20 10 0-4 -3-2 -1 0 1 2 3 4 Difference (%)

IMRT QA results 80 Number of cases 60 40 20 0 0 5 10 15 20 Fraction with γ > 1 for 3%/3mm (%)

Daily QA device Beam Checker Plus signal 8 x 107 7 6 5 4 3 2 1 10F 2400 MupMin 10F 400 MupMin Saturation! 0 0 50 100 150 200 MU

Varian engineer fixing UAB TrueBeam

Machine performance check

AAPM TG-142

Orthogonal kv images

Cone beam CT

MV image

Gantry sag

Difference between automatic and manual

Automated QA Consortium Jeremy Booth & Mario Perez Tim Ritter Hania Al-Hallaq & Karl Farrey Courtesy Jean Moran Todd Pawlicki & Grace Kim Toby Eckhause, Don Roberts, Brett Schultz & Jean Moran John DeMarco Richard Popple Vijeshwar Sharma & Sung Park TBD via Dan Low

Phase 1 QA Test Suite Standardize tests and QA test suite so to evaluate the performance of TrueBeam linacs and compare our results across multiple institutions Use both trajectory log files and EPID measurements (a) (b) Courtesy Jean Moran

Example Fields of QA Test Suite Courtesy Jean Moran + picket fence for VMAT with variable gantry speed, variable gantry speed and dose rate Both HDMLC and Millennium MLC supported

Automated QA Analysis Software analysis developed in MatLab primarily developed by Toby Eckhause (former post-doc) Test suite takes ~15 minutes to deliver; 1 flood field + enter room once to setup phantom All analysis from the original test suite is automated and results can be exported Less than a minute to analyze all data Courtesy Jean Moran

Leaf Position Deviation A (µm) -10-5 0 5 10 0 20 40 Trajectory Log File & EPID Analysis 6 4 2 0-2 -4-6 Leaf Position Deviation(µm) 4 2 0-2 -4-6 mean min max -8-10 -5 0 5 10 Leaf A Position (cm) Leaf Deviation Stdev(µm) 2 1.9 1.8 1.7 1.6 1.5 1.4-10 -5 0 5 10 Leaf A Position (cm) Test suite included all MLC monthly tests in Table V of TG 142, VMAT tests, plus imaging tests. Analysis of Trajectory Log Files Courtesy Jean Moran Maximum difference for leaf position accuracy From Phase 1 of our project with 8 linacs measured over 6 months

Questions?